Redox control on the oxidation state of bridgmanite and CF phase in basaltic assemblages and the origin of retrograde bridgmanite inclusions

Experimental determination of phase equilibria at high pressure and high temperature is pivotal to interpreting geophysical and geochemical data that can help decipher the mineralogical composition of the Earth’s deep interior. Oxygen fugacity is one of the key variables affecting the stability of minerals at high pressure and temperature as it sets the oxidation state of Fe in a given mantle phase assemblages. We propose to use synchrotron Mössbauer spectroscopy to study the oxidation state of Fe in (Mg,Fe2+,Fe3+,Al)(Si,Al,Fe3+)O3 bridgmanite and CaFe2O4-type aluminous phase [(Na,Mg,Fe2+)(Si,Al,Fe3+)2O4] synthesized at conditions of the shallow lower mantle under controlled oxygen fugacity in a multi-anvil press. Results will help inform geophysical and geochemical observations and interpretations, from seismic anomalies associated with the presence of subducted oceanic lithologies in the lower mantle to the crystal chemistry of retrograde mineral inclusions in super-deep diamonds.